Advance of life quality has made people more demanding on lighting and ambient aesthetics. In the past lighting fixtures mostly are exposed outside the construction wall panels that spoiled overall aesthetic design. In recent years downlights wedged in the construction wall panels with only light projection elements exposed outside the decorative surfaces of the construction wall panels have been developed and marketed to provide some improvement. For instance, R.O.C. patent No. 1360621 discloses a downlight which includes a latch member or an elastic element to provide a retaining force to wedge the downlight in a construction wall panel. The elastic element is an elastic arm. Nowadays lighting fixtures using LED as the main light source generally have a heat dissipation element to disperse waste heat generated by the LED, such as a heat sink in the aforesaid patent. To enable the heat dissipation element to achieve desired cooling effect, it is commonly made of high heat conductive material, such as iron, aluminum, copper or alloys thereof. The heat dissipation element thus made is quite heavy and its latch structure cannot provide sufficient retaining force after a long-term period of time to bear such heavy heat dissipation element. As a result, the downlight is prone to wobble and cannot be firmly mounted onto the construction wall panel, or even the downlight could easily loosen away from the installed location. Moreover, the weight of the heat dissipation element also limits the amount of the retaining force generated by the latch structure.
These days the heat dissipation element and light emission element generally are coupled together via a set of fastening elements, such as rivets or screws, and a flat cooling contact surface is formed between them to transmit the waste heat generated by the light emission element to the heat dissipation element. Such a structure tends to generate deformation on the fastening elements because of the heat and results in alteration of the cooling contact surface to decrease cooling efficiency. If this problem is not properly fixed, the waste heat accumulates in the light emission element and could cause heat exhaustion or other problems to the light emission element. How to overcome the aforesaid problems and improve the existing downlights are still issues needed to be resolved.